Multidiode coincidence detector



Aug. 24, 1965 D. B. .JAMES 3,202,983

MULTIDIODE GOINCIDENCE DETECTOR Filed Dec. 8. 1960 CURRENT VOLTAGE E" /NI/EA/TOR By 0. B. JAMES ATTOR'A/Ev information state.

United States Patent O M' 3,202,933 MULTIDIODE CUINCIDENCE DETECTOR Dennis B. James, Bernardsviile, NJ., assigner to Bell Telephone Laboratories, Incorporated, New York, NX., a corporation of New York Filed Dec. 8, 1960, Ser. No. 74,714 12 Claims. (Cl. 340-347) This invention relates to coincidence detection and more particularly to the application of such detection to the conversion of encoded information signals by the employment of negative resistance diodes.

Although an information signal generally originates as a continuous message wave, it is often advantageous to encode it by sampling the wave and transforming the samples into trains of pulse signals. For a given train the constituent pulse signals may be taken in time sequence on a single path, in which case the sampled information signal is said to be serially encoded, or the pulse signals may be taken simultaneously on separate paths, in which case the sampled information signal is said to be parallel encoded. Once encoded, the information signal is subjected to processing. This may require a code conversion from serial to parallel form. Or, it may involve a speed conversion from one pulse rate to another. On occasion it entails time conversion for which the code signals are held in storage for a prescribed delay interval. Accordingly, it is an object of the invention to facilitate Vthe accomplishment of the above mentioned conversions.

A concurrent object is the realization of all such conversions in a single device.

Typically, the conversions have required tandem connected stages which, commencing with the lirst stage, are successively set by serial code signals with information states that are sequentially shifted to succeeding stages. Under these circumstances, the rate at which the code signals can be accommodated by the stages depends upon the rate at which shifting can take place. Consequently, it is a furtherfobject of the invention to eliminate the need for shifting by having each pulse signal of the train act upon but a single stage. A related object is to use the time intervals between the occurrence of the individual pulse signals for directing each of those signals to its appropriate stage which is constituted of a negative resistance diode.

The invention is characterized by the employment of a transmission path whose conductors are interconnected at prescribed intervals by negative resistance diodes. The diodes are so biased that each is capable of adopting any one of at least two distinctive signal states. Initially, all of the diodes are set with a like one of their signal states, for example, their low signal states, and input signals of appropriate polarity areapplied at one extremity of the path. At least one setting pulse signal of the same polarity is applied to the other extremity of the path. The diverse signals then propagate in opposite directions along the path. Whenever oppositely propagating ones of the signals coincide at the position of a diode, that'diode is switched to its high signal state to indicate'a change in its After the desired coincidences have been registered, the diodes so affected are returned to their low signal states by a propagated resetting pulse signal, which may be of opposite polarity from that used in setting. When the input signals represent serially encoded samples, the outputs of the diodes, taken through a conversion network, are either inthe form of parallel vconverted pulse signals or serial pulse signals that have been speedor time-converted.

The accomplishment of the above and related objects will be apparent after the consideration of an illustrative 3,202,983 Patented Aug. 24, 1965 embodiment of the invention taken in conjunction with the drawings in which:

FIG. l is a schematic circuit diagram showing a coincidence detector employing a multiplicity of negative resistance diodes; and

FIG. 2 is a current voltage characteristic of a single diode employed in the detector of FIG. 1 and explanatory of the way in which coincidence detection takes place according to the invention.

Turn now to FIG. 1 showing a dual conductor transmission path 10 of a coincidence detector. At its leftand right-hand extremities, the path 10 is matched in its characteristic impedance by the composite effect of terminating resistors 11-1 through 11-4. Also included at the extremities are various sources 12-1 through 12-3 of pulse signals. Along the path 10 and at each of a number of positions that are equally spaced for convenience the conductors 10-1 and 10-2 are interconnected by the series combination of a biasing resistor 13 and a voltagecontrolled negative resistance diode 14. The diodes 14-1 through 14-11 are collectively biased by a positive-polarity voltage Er which is provided by a signal source 15 that is connected to one of the path conductors, namely, conductor lll-1, through a coupling inductor 16. Individual leads 17-1 through 17n link the anodes of the several diodes 14-1 through 14-n to a converter network 20 which has a series output 21 for speedand time-convetted signals and parallel outputs 22-1 through 22-n for code converted signals. The parallel outputs 22-1 through 22-n .terminate extensions of the individual leads l17-1 through 17-n. Each extension path advantageously includes a differentiating capaci-tor 23, a converter switch `24 and a delay element 25. The series output 21 terminates Ia path that advantageously encompasses all of the switches 24-1 through 2li-n, as interconnected in successive pairs Iby a variable delay element 26 in series connection with a rectifying diode 2'7.l

To understand the operation of the coincidence detector, refer to the current voltage characteristic in FIG. 2 of a representative voltage-controlled diode 14 in FIG. 1. The characteristic displays rst and second regions a and b of positive resistance and an intervening region c of negative resistance. Also depicted in FIG. 2 is the load line d attributable to the biasing resistor 13 associated with the representative diode 14. The load line d, whose slope is the reciprocal of the resistive magnitude of the biasing resistor 13 and whose abscissal location is given by the magnitude of the reference voltage Er, is adjusted until it intersects the diode characteristc in both the first region a and the second region b of positive resistance. For this condition the diode 14 is said to be biased for bistable operation. Initially each diode 14 of the detector in FIG. 1 is in its equilibrium low voltage state determined by the intersection e of the load line d with the .first region a of positive resistance. This intersection e is chosen to be sufficiently far below the threshold f terminating the first region a of positive resistance that the concurrence of two pulse signals is required and suices ,to shift the load line d beyond the threshold f and thus cause the diode 14 to assume its equilibrium high voltage state determined by the intersection g of the load line d with the second region b of positive resistance.

Assume that the source 12-3 at the left-hand extremity of the path 10 in FIG. 1 applies serially coded pulses to the rst conductor 1li-1. Then setting requires the propagation of pulse signals from the opposite extremity of the path 10. These setting pulse signals are of like polarity with the code pulse signals if they originate at the source 12-1 connected to the rst conductor 10-1, or, they are of opposite polarity if they originate at the source 12-2 connected to the second yfor transmission lines, the spacing between successive pairs of diodes ld-l through 14-n is advantageously one-half of the product of the velocity v and the interval t between repetitions of the pulse signals. In this way pulse signals originating, for example, at the setting source y 12-1 are able to set each diode 14 in turn.

Assume that the setting source 12-ll is activated by or synchronized Ywith the lirst pulse signal p-l of the train of pulses occupying at least rst and second code `positions and emanating from the pulse source 12-3 in FIG. 1. Then the rst pulse signal p-l and the setting pulse signal s arrive at the last diode 14E-l simultaneously. At that instant the second pulse signal p-Zy of the train reaches the second from the last diode 14-3, so that by the time the second pulse signal p-Z has travelled to the position of the next to the last diode it-2', the setting pulse signal s is coincident with it. I

For each diode 14 at the position of a coincidence there `is a change in signal state that follows a locus m of increasing voltage shown in FlG. 2L Since the change in signal state is a transient effect, the increasing voltage locus m has a slope which is governed .by the transient impedance seen from the position of the diode 1li. That impedance is but slightly greater than that of each biasing resistor i3 ywith the result that the locus m substantiallyv parallels the load line d. Thus, a complete traversal of the path t@ by the setting pulse s results in the storage of information states in the successive diodes 14-ll'through 14-n`according to the encoding of the pulse train emanating from the pulse source 12-3.

The change in signal state caused by each coincidence is prevented from affecting the reference voltage source "t5 by the isolation afforded by the coupling inductor le. Y Reverse propagation is prevented through the selection of the biasing impedance resistive magnitudes to be substantially greater than the characteristic impedance of the path. Y n y Detection of the stored information Vstates is accomplished through the propagation of a resetting pulse signal r which, when it originates at the second signal source 12,-2, is of like polarity at the setting pulse signal s. Its magnitude is sutciently great to overcome the attenuation of the path i0 so that the diode operation follows the decreasing voltage locus n of FIG. 2,

even atthe left-hand extremity of the path 10. Alteri natively the resetting pulsesignal may be of the op-' 'posite polarity from that used for setting'Lin which case it is applied to the tirst conductor lil-ll of the line.

For serial to parallel conversion the converted signals advantageously occur simultaneously at the par-v Vallel outputs 22-1 through 22-11 of the converter network Ztl. Y T heY appropriate time delay required to compensate for the time required for the traversal of the resetting pulse signal rwis obtained by adjusting the delay elements 25-1v through ZS-n of the parallel paths.v ln l 'order'that the outputs 22-1 through ZZ-n be in the form of pulse signals, the capacitors 231fthrough 23-n act in concert with the characteristic impedances of the paths to dilferentiate the changes in signal level associated with -changes in information state.

To obtain a speedor time-converted set of signals at the Serial output 2l 0,1" ,the `Converter network 20, the

kconverted pulse signals are to appear at the serial output 2l. When the time delay accorded by the rst such element 26-2is equal to the propagation time between the last diode d-l and the last but one lle-2, the converted signals appearing at the serial output 2l occur at the same rate as they are stored in the iirst place.V

By changing the delay time the rate can be increased or decreased accordingly. Besides serving the differentiating function already discussed in conjunction with the parallel path, the capacitors 23-1 through 23-n also serve to isolate succeeding and preceding diode stages from each other.

It is also apparent that the converter may be used to establish differences in the times of origin of diverse pulse signals by noting which `one of the diodes 14-1 through llt-n is caused to change state `when oppositely propagated pulse signals are applied to the transmission path l0. Other uses of the converter and techniques for energizing, monitoring and biasing the path l() will occur to thoseslrilled in the art.

What is claimed is:

1. Apparatus for detecting the coincidences of diverse pulse signals, which comprises a transmission path having two opposite extermities and capable ofy propagating extremity of said path, a pluralityof bistate diode means,

Veachcharacterized by a first signal state and a second signal state and eachv being aflixed to said path at a distinct one `of various positions therealong, andl means coupled to said path for biasing all of said bistate means to their st `signal states and so proportioned that simultaneous `concurrences of pulse signalsfrorn said rst and second groups at said various positions cause the bistate means there positionedrto adopt their second signal states.

2. Apparatus for detecting the coincidences of diverse pulse signals, which comprises a transmission path having two opposite extremities and capable of propagating pulse signals from either extremity tothe opposite extremity, means for applying a iirst group of the pulse signals to one extremity of said path, means for applying a second group of the pulsesignals to the other extremity of said path, a plurality of bistate diode means, each characterized by alirst signal state and a second signal state and each being aliixed to said path at a distinct one of various lpositions therealong, means coupledto said path for biasingall of said bistate means to their Vvfirst signal states and so proportioned that simultaneous concurrences of pulse signals from saidl rst and second Vgroups at said various positions cause the bistate Vmeans n there positioned to adopt their second signal states, and means for applying, at an extremity of said path, a kthird group of pulse signals, whereby the various ones of said bistate means having adopted said second signal states are returned to their rst signal states.

3. Apparatus as defined in claim 2, further including means for convertingthe signal states adopted byl said `bistate means into simultaneously occurring pulse signals which appear on distinctive ,output leads, thereby Vto derive a parallel vencoded counterpart of serially encoded pulse signals applied at one of the extremities ofY said path.y j Y 4. Apparatus as delned in claim 2, further including means, with a separate'connection to each of said bistate means, lfor vconverting signal states adopted by said bistate means into a sequence ofV pulse signals appearing on a distinctive output lead therebyfto derive the delayed counterpart of serially encoded pulse signals applied at one of the extremities of said path.

5. Apparatus as defined in claim 1, wherein said bi state means comprises a negative resistance means and loading means connected in series therewith.

6. Apparatus as defined in claim 5, wherein said negative resistance means comprises a voltage-controlled negative resistance diode and said loading means comprises a resistor.

7. Apparatus as defined in claim 3, wherein said conversion means comprises means for individually dir'erentiating the signal levels associated with said adopted signal states to obtain distinctive pulse signals, and means for delaying the pulse signals thus obtained.

8. Apparatus as defined in claim 4, wherein said conversion means comprises means for individually difierentiating the signal levels associated with said adopted signal states, a multisegmented output path, each segment of said path including delay means and means for inhibiting back propagation, and means connecting successive ones of said dierentiating means to successive segments of said path.

9. Apparatus for deriving a group of output Voltage levels from a serially encoded group of input pulse signals, which comprises a dual conductor transmission line, means for matching said line in its characteristic impedance at each of its extremities, means for applying the input pulse signals at one of said extremities, means for applying setting pulse signals at the other of said extremities, a plurality of paths, each interconnecting the conductors of said line ata distinct one of equal intervals therealong and including the series combination of a voltage-controlled diode and a biasing resistor, said diode displaying a current voltage characteristic with a rst region of positive resistance terminated in a threshold and separated from a second region of positive resistance by an intervening negative resistance region, said resistor having a resistive magnitude greater than the minimum of such magnitude identifiable with said intervening region of negative resistance and providing a load line that intersects said characteristic, and means connected to one of said conductors for collectively biasing the diodes to equilibrium voltage levels substantially determined, for each diode, by the intersection of said load line with the first positive resistance region of said characteristic and for simultaneously causing the intersection of said load line with the second positive resistance region of said characteristic, whereby the coincidences of said input signals and said setting pulse signals at various intervals along said line causing the thresholds of the diodes there located to be exceeded result in the setting of those diodes with output voltage levels substantially determined by said intersection of the load line with said second positive resistance region.

10. Apparatus for deriving a parallel encoded group of output pulse signals from a serially encoded group of input pulse signals, which comprises, in combination with apparatus as dened in claim 9, means for applying resetting pulse signals at one of said extremities, a plurality of output paths, respective ones of said paths being connected to respective anodes of said diodes, each of said paths including a capacitor and a delay element connected in series with said capacitor, whereby the occurrence of a resetting pulse signal at the position of the diode that has been set with an output voltage level causes that diode to return to its equilibrium voltage level and provide an output pulse signal on the path connected to its anode.

11. Apparatus for converting a serially encoded group of input pulse signals with a iirst repetition rate into a delayed and serially encoded group of output pulse signals with a second repetition rate, which comprises, in combination with apparatus as defined in claim 9, means for applying resetting pulse signals at one of said extremities, a delay path with a plurality of taps extending therefrom, said path including between each pair of taps the series combination of a delay element and a rectifying diode, and a plurality of capacitors, respective ones of which interconnect respective ones of said taps with respective anodes of said diodes, whereby the occurrence of a resetting pulse signal at successive positions of diodes that have been set with output voltage levels causes the diodes so set to return to their equilibrium voltage levels and launch on said delay path a serial group of output pulse signals with a repetition rate determined by the adjustments of said delay elements.

l2. Apparatus for deriving a group of output signal levels from a group of input pulse signals, which comprises a dual-conductor transmission line, means for matching said line in its characteristic impedance at each of its extremities, means for applying the input pulse signals at `one of said extremities, means for applying an auxiliary signal at the other of said extremities, a plurality of negative resistance diodes interconnecting one conductor with the other at distinct intervals along said transmission line, and means, connected to one of said conductors, initially biasing said diodes to one signal level and subsequently biasing each diode at the coincidence position of said input and auxiliary signals to another signal level.

References Cited by the Examiner UNITED STATES PATENTS 2,593,948 4/52 Wiegand et al. 328--94 2,711,526 6/55 Gloess 340-167 2,992,339 7/61 Meyers 307-885 FOREIGN PATENTS 759,139 10/56v Great Britain.

MALCOLM'A. MORRISON, Primary Examiner.

STEPHEN W. CAPELLI, Examiner. 

1. APPARATUS FOR DETECTING THE COINCIDENCES OF DIVERSE PULSE SIGNALS, WHICH COMPRISES A TRANSMISSION PATH HAVING TWO OPPOSITE EXTERMITIES AND CAPABLE OF PROPAGATING PULSE SIGNALS FROM EITHER EXTERMITY TO THE OPPOSITE EXTREMITY, MEANS FOR APPLYING A FIRTS GROUP OF THE PULSE SIGNALS TO ONE EXTREMITY OF SAID PATH, MEANS FOR APPLYING A SECOND GROUP OF THE PULSE SIGNALS TO THE OTHER EXTERMITY OF SAID PATH, A PLURALITY OF BISTATE DIODE MEANS, EACH CHARACTERIZED BY A FIRST SIGNAL STATE AND A SECOND SIGNAL STATE AND EACH BEING AFFIXED TO SAID PATH AT A DISTINCT ONE OF VARIOUS POSITIONS THEREALONG, AND MEANS COUPLED TO SAID PATH FOR BIASING ALL OF SAID BISTATE MEANS TO THEIR FIRST SIGNAL STATES AND SO PROPORTIONED THAT SIMULTANEOUS CONCURRENCES OF PULSE SIGNALS FROM SAID FIRST AND SECOND GROUPS AT SAID VARIOUS POSITIONS CAUSE THE BISTATE MEANS THERE POSITIONED TO ADOPT THEIR SECOND SIGNAL STATES. 